The present invention relates to a process for recovering gas oil or fuel oil from topped crude oil. More particularly the present invention relates to a process for recovering a substantially asphalt-free fuel oil from a topped crude oil, the asphalt-free fuel oil being usable as a feed to a commercial hydrodesulfurization unit.
In the refining of crude oil, it is common practice to atmospherically distill the crude oil to recover various fractions of gases, gasoline, kerosene, gas or fuel oil, etc. The heavy, residual material remaining from the atmospheric distillation, commonly referred to as topped crude oil, can vary in amount but may comprise up to about 40% by volume of the original crude oil and contains the asphalt originally present in the crude oil. The heavy, residual material can be further treated by vacuum distillation to recover additional quantities of gas oil and provide a residuum, commonly referred to as vacuum reduced crude oil. Vacuum reduced crude oil generally amounts to about 5 to about 25% by volume of the original crude oil. For purposes herein, the term "topped crude oil" shall include the materials defined above as "residual material" and "residuum." It is common practice to treat the topped crude oil, as for example by extraction techniques, to produce an asphalt suitable for uses such as an asphalt cement for road construction, and recover further fuel oil. Such a process is described in U.S. Pat. No. 3,658,695.
To render the recovered fuel oil suitable for end uses, it is often desireable that it be desulfurized by treatment in a hydrodesulfurization unit or the like. Depending on its origin, crude oil contains in the range of from about 20 to about 9,000 ppmw (parts per million by weight) metal contaminants such as compounds (many of unknown type) of nickel and vanadium. In the refining processes described above, the metal contaminants tend to concentrate in the topped crude oil and appear in sufficient concentration in the fuel oil recovered therefrom to poison or at least greatly reduce the life of the catalyst used in the commonly employed hydrodesulfurization processes.